diff --git a/src/checkstyle/com/puppycrawl/tools/checkstyle/TreeWalker.java b/src/checkstyle/com/puppycrawl/tools/checkstyle/TreeWalker.java
index 75e674ea7..f2b391865 100644
--- a/src/checkstyle/com/puppycrawl/tools/checkstyle/TreeWalker.java
+++ b/src/checkstyle/com/puppycrawl/tools/checkstyle/TreeWalker.java
@@ -130,8 +130,13 @@ class TreeWalker
     {
         mMessages.reset();
         notifyBegin(aContents);
-        aAST.setParent(null);
-        process(aAST);
+
+         // empty files are not flagged by javac, will yield aAST == null
+        if (aAST != null) {
+            aAST.setParent(null);
+            process(aAST);
+        }
+
         notifyEnd();
     }